AT&T mobile network website DNS cache

I am an AT&T mobile customer. I have a website.

I recently moved my website to a new web server, and DNS updated accordingly by the hosting company. It also has new web files and web design.

The updates have propagated throughout the web, with the exception of AT&T's mobile network which displays the old site on the old server (which is still up, out of my control).

I have tried:

- different devices

- incognito browsers

- devices that have never seen the site before

- killing the new server and moving to a new IP with fresh files

- every 301 redirect imaginable

- waiting days, weeks on end (going on 2 months now)

I have been working with the hosting company and they have tracked the issue to AT&T's mobile network DNS cache.

My question is - HOW can I get AT&T to update their DNS cache??